In terminating an output of electronic circuits, there are a few common approaches. Examples approaches are demonstrated in FIGS. 1A and 1B where the circuit is DC terminated by either pulling the output to ground, as shown in FIG. 1A, or pulling the output to a supply voltage VDD, as shown in FIG. 1B. In these examples, the pull-up or pull-down resistor is labeled as RRX. The DC termination typically provides good performance and return loss across all frequencies. Nevertheless, DC termination is generally avoided in circuits requiring low power due to the higher power consumption at the transmitting (TX) driver. DC termination also typically requires a reference voltage Vref for defining the receiver (RX) slicing point (not shown) which also may change with swing of the output. This problem may be resolved with a simple resistor-capacitor (RC) circuit. However, at low data rates, such solution may exhibit problems with consecutive identical digits (CIDs). DC termination also typically exhibits an asymmetry in the eye (e.g. rise and fall times are different), which may cause the transmitter to also exhibit asymmetric properties.
Another approach to terminating the output of electronic circuits is AC coupled termination as demonstrated in FIGS. 1C and 1D. The approach presented in FIG. 1C provides AC termination that resolves some of the power consumption problems of DC termination by requiring only half the power. AC termination also requires no generation of a reference voltage. However, AC termination typically suffers from DC wander. As well, tracking CIDs, particularly at low data rates, typically requires a large capacitor (which may be too large for practical implementation). Further, AC termination may have poor low frequency termination.
The DC wander exhibited by FIG. 1C may be corrected by adding a voltage regulator 102, as shown in FIG. 1D. However, this is at the cost of higher power consumption for both the TX driver and RX regulator for singled-ended receiving. The voltage regulator 102 also requires area on the semiconductor device. The voltage regulator 102 may also become unstable in certain instances.